The sources of noise in a readback signal from a magnetic recording medium have been investigated and identified. One of those sources includes the irregularities and defects in the microstructure of the magnetic medium itself. For many years, the noise generated from this source has been thought, as with the noise generated from other identified sources, to be random and subject only to statistical analysis for its determination. The inventors herein have recently demonstrated that this noise component is instead deterministic, i.e. is permanent and repeatable, depending entirely on the head-medium position and on the magnetic history of the medium. As confirmed by experiments conducted by the inventors herein, when the medium has had no signal written on it and has been exposed only to DC fields, the observed readback signals are almost identical. The magnetic contribution to the readback signal under these conditions results from spatial variations in the medium's magnetization: magnetic domains, ripple, local fluctuations of the anisotropy field and saturation magnetization. These local properties, in turn, are affected by the morphology and magnetic properties of the individual grains which make up the domain and which do not change after deposition. Hence, the noise from a nominally uniformly magnetized region measured at a fixed position on a magnetic medium is reproducible. As shown by the inventors herein, a magnetic medium may be DC saturated and its output then measured to determine its remanent state or remanent noise. The inventors have confirmed that this remanent noise is a function of the magnetic microstructure by comparing the remanent noise after a positive DC saturation with the remanent noise after a negative DC saturation. It has been found that these wave forms are virtual "mirror images" of each other thereby demonstrating a close correlation. Similarly, other methodologies were used to confirm that the remanent noise was deterministic, repeatable, and related to the physical microstructure of the magnetic medium itself. Remanent noise arising from the permanent microstructure exhibits identifiable features characteristic of that permanent microstructure after practically any magnetic history. See Spatial Noise Phenomena of Longitudinal Magnetic Recording Media by Hoinville, Indeck and Muller, IEEE Transactions on Magnetics, Volume 28, No. 6, November 1992, the disclosure of which is incorporated herein by reference.
There is a long felt need in the art for a method and apparatus to identify or fingerprint various kinds of documents as well as the wide variety of prerecorded magnetic media presently being marketed and/or distributed in the United States and throughout the world. Examples of these magnetic media include those produced and sold in the entertainment industry including magneto-optic discs and tapes, cassette tapes, reel to reel tapes, videotapes, etc. Still another major market in magnetic media is the tremendous volume of computer programs routinely sold and/or distributed on floppy diskettes. Magnetic media are also used for other purposes for which it is important to be able to identify and authenticate originals including videotapes, cassette tapes, and other prerecordings on magnetic media of telephone conversations, video recordings of criminal activities, and other such investigative and documentary uses. Still another example of a need in the art for authentication and verification of magnetic media lies in the magnetic data card field. Examples of magnetic data cards include the well known credit card as well as ATM cards, debit cards, security or ID cards, mass transit cards, and even airline tickets or other vouchers which have magnetic stripes thereon for the magnetic recording of data. As well known in the art, virtually every magnetic data card has a magnetic stripe of prerecorded magnetic data which is used to record the customer's account number or some other such identifying data. Tremendous sums of money are lost annually through forgery and other fraudulent copying and use schemes which could be virtually eliminated if an apparatus and methodology could be implemented for reliably authenticating and verifying the identity of a magnetic data card prior to its being approved for its associated transaction. Still other examples extend to paper documents and the like for which there has been some specific efforts of which the inventors herein are aware.
As related in an article entitled Novel Applications of Cryptography in Digital Communications by Omura, IEEE Communications Magazine, May 1990, a technique is disclosed for creating counterfeit-proof objects. As related therein, the basic idea is to measure some unique "fingerprint" of the paper and to sign (encrypt) it using the secret key of the manufacturer of, for example, a stock certificate. The fingerprint is obtained by moving a narrow intense light beam along a line on the paper and measuring the light intensity that passes through the paper. The light intensity function determined by the unique random pattern of paper fibers along the line then forms the fingerprint of the particular piece of paper. This fingerprint is then digitized and encrypted by the secret encryption function. The encrypted fingerprint is then separately printed onto the paper in digital form such as a bar code. At a later date, the authenticity of the stock certificate may be verified by using a non-secret public decryption function to decrypt the encrypted data on the paper and reconstruct the intensity function, or fingerprint, that was recorded thereon. Next, the actual intensity function of the stock certificate is measured. If this newly measured intensity function agrees with the intensity function reconstructed from the decrypted data, the document may be declared authentic. This scheme takes advantage of a well know secrecy system referred to as a public key cryptosystem. This system employs a trap door one way function. A user chooses a secret key (the trap door) and after applying the trap door one way function to the data, the procedure determines an algorithm used for decoding which is made publicly known. The trap door one way function is also used to produce the encrypted message. Then every other user can understand the original message by applying the algorithm to the cryptogram. In this system no one else can produce a publicly readable message attributable to the original user's trap door as only the user has knowledge of that algorithm. This prevents the simplistic forgery attempt of changing the pre-recorded fingerprint to agree with a forged document's fingerprint.
Still another example of an attempt in the prior art to fingerprint or counterfeit-proof objects is shown in U.S. Pat. No. 4,806,740. As shown therein, an object, such as a stock certificate, has deposited thereon a stripe of magnetic medium having a variable density resulting from the non-uniformity of the paper, the process of depositing the magnetic medium on the document, and the dispersion of magnetic particles within the medium. The density variations are randomly created as the magnetic medium is applied, which affords a unique document as these density variations are fixed and repeatable to identify the document. A second magnetic stripe is also applied to the document, but this magnetic stripe is comprised of a medium that is tightly specified and highly controlled in accordance with well known standards in the recording art to be part of a magnetic read/write system. In operation, the non-uniform magnetic stripe is erased, recorded by a standard recording comprised of a linear DC signal or a linear AC signal or a linear bias signal. After recording, another head senses the magnetic characteristic of the recorded magnetic stripe which is translated into a digital, machine readable format, and then separately recorded on the second magnetic stripe in a simple write function. For authentication, the stock certificate is passed under another set of heads which first reads the digitally recorded machine readable representation of the sensed noise signal and then a second set of heads reads the variable density magnetic stripe by first erasing it, recording the same standard noise function, and then sensing the output of the prerecorded noise function as it is "distorted" by the variable density magnetic stripe. If it matches the recorded representation thereof, then the document is declared to be authentic and original. Thus, with the method of the '740 patent, a pair of magnetic stripes must be applied to the document and a specified signal (denominated as noise) must be recorded, measured, and then its output digitally recorded. Furthermore, one of the magnetic stripes must be applied in other than recording industry standard and in a random manner to ensure the randomness of the output thereof. These steps make the '740 patent method difficult and inconvenient to implement.
Yet another example of a prior art attempt to utilize a magnetic fingerprint of a magnetic medium for authenticating credit cards, documents, and the like is found in Pease et al U.S. Pat. No. 4,985,614 issued on Jun. 15, 1991. This '614 patent is actually quite similar in concept to the '740 patent discussed above in that it focuses on the macroscopic, hereinafter denoted "macro" variations in a magnetic medium, and their effect on an "enhancing" signal recorded thereon in one embodiment or standing alone in a second embodiment. With either embodiment, these "macro" variations are determined by reading a chosen length of approximately 2.6 inches of a magnetic stripe between 3 and 9 times (5 in the preferred embodiment) and then correlating the collected data points to "average out" the effects of head noise, electrical noise, and any other non-medium noise. This correlation results in a "representative profile" which represents the variances which would be induced by these macro effects to a signal if it were recorded on this 2.6 inch portion of magnetic stripe. If these variations are not significant enough to produce a reliable correlation, indicating a lack of significant macroscopic nonuniformities in the medium, the medium is discarded. This is an indication that the medium has been manufactured too closely to tolerance, or otherwise does not have enough macro level variation which might be present due to a manufacturer's watermark or the like, to induce reliably detectable and repeatable variations to a recorded signal. The '614 patent also suggests that macro level noise may be enhanced by locally altering the apparent magnetic characteristics of the stripe such as by placing magnetic symbols on the substrate underlying the magnetic region, or by embossing selected regions of the magnetic material so as to physically move some amount of the material. As the noise levels measured have significant effects on the peaks of a recorded enhancing signal, a simple peak detect and hold circuit is taught as sufficient to collect the data, and a simple "comparison" of the pre-recorded "representative profile" with the presently sensed data points is taught as sufficient to determine if the medium is authentic. Therefore, not only does the '614 patent focus on the use of macro level noise, its device and methodology disclosed for implementing a macro level noise detector is believed to be incapable of reliably creating a microstructure noise level fingerprint and validating its existence at a later time in order to authenticate an original.
In order to solve these and other problems in the prior art, the inventors herein have developed a method and apparatus for utilizing the unique, deterministic, remanent noise characteristic of the magnetic medium itself due to its magnetic microstructure to fingerprint not only documents, but other objects and more importantly, the magnetic medium itself so that it can be identified and authenticated. This inventive technique relies upon the discovery that the microscopic structure of the magnetic medium itself is a permanent random arrangement of microfeatures and therefore deterministic. In other words, once fabricated, the recording medium's physical microstructure remains fixed for all conventional recording processes. In particulate media, the position and orientation of each particle does not change within the binder for any application of magnetic field; in thin film media, the microcrystalline orientations and grain boundaries of the film remain stationary during the record and reproduce processes. It is the magnetization within each of these fixed microfeatures that can be rotated or modified which forms the basis of the magnetic recording process. If a region of a magnetic medium is saturated in one direction by a large applied field, the remanent magnetization depends strongly on the microstructure of the medium. This remanent state is deterministic for any point on the recording surface. Each particle or grain in the medium is hundreds to thousands of Angstroms in dimension. Due to their small size, a small region of the magnetic surface will contain a very large number of these physical entities. While the fabrication process normally includes efforts to align these particles, there is always some dispersion of individual Orientations and positions. The actual deviations will be unique to a region of the medium's surface making this orientation a signature or a "fingerprint" of that medium. To reproduce this distribution, intentionally or not, is practically impossible since this would entail a precise manipulation of the orientation of numerous particles at the submicrometer level. Thus, the orientation of a large set of particles on a specific portion of a recording surface can uniquely identify that medium. In experiments, the inventors have found that the remanent noise from a length of between about 30 micrometers and 4300 micrometers provides enough data to "fingerprint" a magnetic medium. This may be contrasted with the 66,040 micrometers (2.6 inches) of length required in the '614 patent in order to fingerprint a magnetic medium with macro noise.
In essence, the present invention is elegantly simple and adapted for implementation by conventional recording heads as are commonly found and used in virtually every read or read/write device presently utilized by the public at large. Such examples include credit card readers, magneto-optic disc players, cassette players, VCRs and personal computers. Furthermore, a card reader may be coupled with virtually any device or process, and the card reader used as a "Gatekeeper" to permit input or access only by those who can present a valid passcard for authentication. In its simplest implementation, a conventional recording head need merely DC saturate a specified portion of a magnetic medium, and then "read" or "play back" the remanent noise which remains. For convenience, the fingerprint may be obtained from the region between two recorded magnetic transitions already in place on the medium. This remanent noise, which is an analog signal, may then be digitized and recorded, in the medium itself or elsewhere, in machine readable format perhaps using a trap door function. Thusly, the magnetic medium has become "labeled" with its fingerprint. Verification or authentication of that magnetic medium is simply achieved by reversing this process except that in the more security sensitive applications the digitally recorded fingerprint must be decrypted using the publicly known key. Should the measured remanent noise match the remanent noise as recorded, the magnetic medium is authenticated.
There are many variations in utilization of the inventors' method and apparatus which expand its universe of applications. For example, some applications need not require the use of a trap door function such as, for example, when the encoded objects are not publicly distributed and instead are being identified solely for the user's purposes. One such example would be for use with inventory items.
Still another application involves the "copy protection" of mass distributed application software. Over the years, many schemes have been tried and almost uniformly abandoned for copy protecting publicly distributed diskettes of prerecorded software. This has happened for many reasons including the problem that almost all of the copy protection schemes previously implemented interfere with the running of the software on the user's computer. With the present invention, a copy protection scheme may be implemented which does not interfere with the running of the software and instead merely provides a precondition to running of what is otherwise normally written code. In its implementation, a software diskette may first instruct the computer in which it is inserted to read a fingerprint of a specified portion of the diskette and compare it with a prerecorded version of the same fingerprint. If the fingerprints match, then the software may permit the computer to further read and implement the application software stored thereon. However, if the fingerprint detected by the computer does not match that which is stored in the software, then the software itself may inhibit further reading of the program and prevent its implementation. This would absolutely prevent a user from making a copy of a program for use by someone else. This scheme may also be slightly modified as discussed in the detailed description of the preferred embodiment to permit a user to make a single archive or backup copy such that the fingerprint comparison permits the first non-matching fingerprint copy to be run but then prevents any other non-matching fingerprinted copies to run. This implementation is easily achieved and "copy protects" application software reliably, inexpensively, and requires only minor hardware changes to the massive number of computers already in consumers' hands.
Still another significant application of the present invention involves authenticating credit cards using the single magnetic stripe already implemented on most major credit cards. Again, this may be contrasted with the '614 patent which suggests that a second stripe be added because of the required 2.6 inches of stripe length which must be dedicated to the macro fingerprint techniques. The same method would be used as explained above to measure and record the "fingerprint" of the particular magnetic stripe contained on a particular credit card and then a credit card reader would require that same fingerprint to be matched every time it is used to verify its authenticity. While there are already a large number of credit cards in circulation, these cards are routinely subject to expiration such that there is a continual replacement of these cards in the public's hands. Thus, over time the installed base of credit cards could be readily transformed to those which have been "fingerprinted".
In a variation to this application, the present invention may be coupled with a data base or processor, such as in so-called Smart Cards. These credit card-like devices actually contain, in addition to perhaps the standard credit card magnetic stripe, an on-board electronic memory and/or microprocessor. This memory or microprocessor may contain all sorts of information including money substitute data. For example, at present a large number of these smart cards are in use in Europe as pre-paid telephone cards which are pre-loaded with a monetary amount which is charged against by a pay phone. The cards are used until their pre-loaded monetary equivalent has been depleted and then they are discarded. While various security methodologies have been developed to protect against fraud, these are subject to breach. The present invention is uniquely suited as a security scheme for smart cards as it depends solely on the magnetic microstructure of the particular magnetic medium. In use, the magnetic fingerprint could be stored on the magnetic stripe, in the smart card memory (on board the card), or in a central computer. When coupled with a trap door function, no fraudulent card could be created without access to the trap door function and every transaction could be quickly pre-authorized at a local card reader, without phoning a central clearing authority. In an extension to all credit card applications, the fingerprint data may be stored along with each transaction so that a complete record or trail is created which traces a particular card's history. Thus, the present commonly used scheme where a number of fraudulent cards are created with a correct but stolen account number could either be thwarted or effectively prosecuted.
Another level of security incorporates random placement of the fingerprint position. This might be a function of the card's number. For example, the card number modulo "P" might point the read electronics to a particular data bit around which the fingerprint will be found.
Still another significant category of applications involves utilizing the present invention in its gatekeeper function. Any system, process, machine, location, or other function to which access is desired to be restricted to only those who are authorized, the present invention provides a unique and reliable solution. In its simplest implementation, a passcard may be created with a magnetic stripe which is fingerprinted in accordance with the present invention. Although examples will be discussed in terms of utilizing a passcard, it should be understood that any magnetic medium can be similarly used in accordance with the teachings herein. As such, all other such examples and implementations are intended to be included within the present invention and shall be understood to be included within the term "passcard". This passcard may then become a personal ID card which may be used not only to control access, but also identify the particular person accessing the service, function, etc. by storing the particular magnetic fingerprint of the card being used. Numerous examples may be readily considered. For example, access to a computer network through a remote terminal may be controlled utilizing a passcard of the present invention. This would be implemented through the use of a diskette which may be readily inserted in any floppy disk drive which could authenticate the fingerprint on the diskette. Alternatively, an inexpensive card reader, adapted to read a passcard, could be utilized as well. Many other applications would utilize the modified card reader. For example, a bank teller may be assigned a passcard which could then be used to track all of the transactions entered by the teller and thereby more reliably guard against teller fraud. The myriad of identification cards utilized by businesses, health plans, universities, hospitals, and other organizations or facilities could readily adopt and use a passcard to more securely identify and preauthorize the users of its services, facilities, etc. Not only would existing uses be readily amenable to replacement with the passcard of the present invention, but other new services and systems could be implemented because of the high degree of security provided by the present invention. This may include home shopping and pay-per-view video. This may well lead to the creation of national data bases, national ID cards, and other more universal implementations of credit cards or passcards. This is especially true if a system utilizes not only the magnetic fingerprint of a particular passcard, but also utilizes a secondary security check such as a picture ID, human fingerprint, hologram (presently imprinted on credit cards), or other such methodology which would thereby render the passcard system virtually impregnable. With such security, individuals may be more willing to turn over such detailed personal financial and health information as would make these systems feasible.
While the principal advantages and features of the invention have been described above, and a number of examples given, a greater understanding of the invention may be attained by referring to the drawings and the description of the preferred embodiment which follow.